In the past few years, a tremendous effort has been made to develop disinfectants that are environmentally-friendly, effective against microorganisms when diluted, and non-toxic to humans and animals. Hydrogen peroxide is environmentally-friendly as its decomposition products, namely oxygen and water, are generally benign. It has been used for many years in various applications due to, at least in part, its broad spectrum of antimicrobial activity. This characteristic is particularly important in situations where harmful organisms are present but their identity is not known.
One of the primary drawbacks of hydrogen peroxide is that its antimicrobial action is too slow at low concentrations. For example, known references indicate that a 0.1% w/w aqueous solution of hydrogen peroxide requires about 60 minutes to disinfect surfaces contaminated with Staphylococcus aureus, whereas, under the same test conditions, a 25.8% w/w aqueous solution of hydrogen peroxide requires only about 20 seconds. The latter solution may not be practical or economically viable. It may be subject to hazardous goods regulations and require special precautions for handling and use. A second major drawback is that stabilizers typically used to stabilize hydrogen peroxide in solution, namely, phosphorus-based stabilizers, may deposit and accumulate in rivers and lakes and contribute to their eutrophication.
Solutions containing less than about 8% w/w hydrogen peroxide are preferred for their improved safety profile. For example, at concentrations of above about 8% w/w aqueous solution, hydrogen peroxide is considered corrosive and a strong oxidizing agent. At concentrations of about 3-7% w/w aqueous solution, hydrogen peroxide is considered non-corrosive but an eye irritant. At concentrations of about 1-3% w/w aqueous solution, hydrogen peroxide is considered non-corrosive and non-irritating.
Attempts have been made to enhance the disinfecting activity of hydrogen peroxide solutions. For example, peracid combined with hydrogen peroxide can increase the disinfectant activity of hydrogen peroxide significantly. However the disadvantage of such compositions is their corrosiveness, poor safety profile, and pungent smell. Increased activity can be also achieved by combining hydrogen peroxide with heavy metals to release hydroxyl radicals. Unfortunately, such solutions demonstrate poor stability, and should be prepared in situ.
Sparingly water soluble cyclic carboxylic acids have been shown to enhance the disinfecting activity of solutions containing hydrogen peroxide and certain anionic surfactants (e.g. dodecyl benzene sulfonic acid). It is possible to make ready-to-use products with a combination of these ingredients, with the cyclic carboxylic acid present in low concentrations. However, making concentrated versions of these solutions is a challenge, due to the low solubility of the cyclic carboxylic acids in aqueous solutions. At higher concentrations, such acids precipitate out of solution. This makes it difficult to prepare diluted, ready-to-use solutions that are of a uniform character and provide consistent performance from the concentrated solution. As concentrated solutions are easier and less costly to ship, it is desirable to make solutions comprising sparingly soluble cyclic carboxylic acids, hydrogen peroxide and anionic surfactants in concentrated form.
One way to do this is to add high quantities of solvent or emulsifiers to solubilize the acid in solution. However, this can be undesirable for the following reasons. Many solvents are considered volatile organic compounds (VOCs) which are not favorable from an environmental point of view. Furthermore, they can serve to reduce the flash point of the solution and increase its hazard rating. Using high levels of emulsifiers can leave a residue that produces streaking and tackiness on surfaces or devices after drying.
Another approach to making concentrated solutions containing a sparing soluble cyclic carboxylic acid, hydrogen peroxide, and an anionic surfactant is to increase the pH to increase the solubility of the acid in solution, partially turning it into its salt form which is more water soluble. However, since such acids tend to act better in their acid form, increasing the pH can reduce the antimicrobial effectiveness of the solution.
There is therefore a need for a stable, concentrated, hydrogen peroxide-based cleaning and disinfecting solution containing one or more anionic surfactants and one or more sparingly soluble cyclic carboxylic acids, which solution can be diluted prior to use. Preferably, the solution is not flammable, does not leave high amounts of residue after being applied to a surface after dilution, and is efficacious and fast-acting at high dilutions.